Exploring Life at Hydrothermal Vents - Planet Earth Online

Clare Woulds, University of Leeds

Hydrothermal vents were only discovered in the 1970s but have turned out to be some of the most fascinating ecosystems on Earth. These deep sea geezers are teaming with unusual life from a species of weird pale octopus to the recently identified 'hoff' or yeti crab as described on our podcast earlier this year. But there are some fundamental questions scientists studying hydrothermal vents don't yet know the answers to.

Clare Woulds at the University of Leeds, for instance, is investigating food webs, what does everything living in the sediments around hydrothermal vents eat. Richard Hollingham went to visit her lab in Leeds where she showed him the samples that she works on...

Clare - I have to ask you not to touch bits of this freezer, because I've got nice big blue insulated gloves on but if you touch it you will get stuck to it and then we have serious problems.

Richard - Phwoar! You can feel the cold, it's like a slice of Antarctica just there - I'm not touching it.

Clare - Ok, I'm going to open this bottom drawer here – so this is the one that my samples are kept in - and these bags of mud are mine, you can hear the crackle, that's just a plastic bag but because it's so cold it sounds really brittle. We’ll take these out and put them on the bench and have a quick look.

Richard - So, we've got frozen sediment samples from where?

Clare - This site is called Hook Ridge, and it’s what we call a defuse hydrothermal venting site. Instead of this rocky bottom with chimneys there is actually a cover of soft sediment or mud over that, so the hydrothermal fluids are coming bubbling out through the mud. That's the type of site that these come from.

Richard - I have to say if we can look through the bag - again, I'm not going to touch that - it just looks like crisp sized bags of frozen mud.

Clare - That is actually what it is, but they're very carefully labelled bag of frozen mud.

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Richard - And appearances can be deceptive because the sediment is full of life...

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Richard - So, we've come into the microscopy lab and appropriately enough, there is a microscope and under there you've got a sizable petri dish.

Clare - This is a sample that was preserved slightly differently. It was pickled, if you like, in formalin and what I've done this morning is I've taken the whole sediment sample and I've sieved it. And what we're looking at is the coarse fraction greater than 250 microns in size, that's a quarter of a millimetre, so still quite small, and we're going to have a look at it under the microscope to see what animals are living in the sediment that we can pick out for analysis.

Richard - Let's have a look... What are you trying to find out?

Clare - I'm interested in carbon cycling. That really means where is the food coming from for this ecosystem and how does that food travel through the ecosystem. So who is eating what and who is eating who else.

Richard - And how are you doing that?

Clare - At a hydrothermal vent system we have a really interesting phenomenon in that the biological community there has two different sources of food. Mostly in the deep sea there's only one source of food and that's food that falls down from the surface ocean from plant production in the surface ocean. At hydrothermal vents there are really interesting microbial communities that can also make food just like plants do at the surface, but instead of using sunlight, because there's no sunlight at 1500 metres in the ocean, they use the chemical energy from all of these strange volcanic fluids seeping out of the sea floor. So this biological community has a choice of two different food types. It can eat algae sinking from the surface of the ocean or it can eat bacteria that are producing food in situ on the seafloor. The thing we don't know is to what extent is this community reliant on those two different types of food, so where is the carbon coming from and how is it being cycled?

Richard - And how are you trying to look at that and investigate that?

Clare - I did some experiments where I collected sediment cores, I collected tubes full of sediment, that had all of their natural structure and their natural biology intact. I then added chemical labels to those cores. Some of that was chemically labelled algae and in different cores I added a chemical label that the in situ bacteria would take up. I'm then going to pick out the animals from these sediment samples and see which animals eat which different type of food.

Richard - And is it quite exciting to be working on something that really we've only started exploring in the last ten to twenty years?

Clare - Yes, that's fantastically exciting. I feel very privileged to be in this position of doing something for the first time. It's really exploratory and that's fantastically exciting.

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